The multiple deformation sensor system for small diameter borehole is required for the long term monitoring of
deformation of rock mass of high-level radioactive waste disposal site. The conventional electric monitoring systems are
difficult to apply for a long term monitoring in many cases because of the sensor failure caused by lowering of insulation
or other problems and only available for the large borehole and for 6 or less measurement sections. The Borehole
Multiple Deformation Sensor System was developed based on the FBG (Fiber Bragg Grating) sensor technology that is
expected to have longer life time than electric systems. The developed system can be set in a 66 mm diameter borehole
and available for 9 or more measurement sections that can be hardly achieved by electric systems. The sensor system is
applying for the monitoring of ground deformation in the Horonobe Underground Research Laboratory in Japan.
The monitoring of slope deformations is often required for management of construction or for disaster prevention. Although various kinds of electrical monitoring systems have been developed, they still have problems on shielding electric noises, waterproofing and so on. An optical monitoring system is expected to solve those problems because it is basically unaffected by electric noises and waterproofed by itself. Borehole inclinometer is one of the typical transducers for slope deformation monitoring. By electrical ones, it is hard to take continuous data of many points in a small diameter borehole. To improve these weak points, we developed the monitoring system with borehole inclinometers using Fiber Bragg Gratings (FBG) as a strain sensor. The transducer consists of series of unit-bars connected each other with elastic joints. FBGs were embedded on the elastic joints, and bending angles of each joint were measured by FBGs. The transducer was set in a borehole, and underground deformations were measured as bend of each joint at a remote monitoring center. We had applied this monitoring system for artificial slope under construction for 4 months. The data obtained by the system indicate the deformation according to a progress of land banking.
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